Chemical isolation and characterization of different cellulose nanofibers from cotton stalks.

Recently, cellulose nanofibers (CNFs) have received wide attention in green nanomaterial technologies. Production of CNFs from agricultural residues has many economic and environmental advantages. In this study, four different CNFs were prepared from cotton stalks by different chemical treatments followed by ultrasonication. CNFs were prepared from untreated bleached pulp, sulfuric acid hydrolysis, and TEMPO [(2,2,6,6-tetramethylpiperidin-1-yl) oxy radical]-mediated oxidation process. Physical and chemical properties of the prepared CNFs such as morphological (FE-SEM, AFM), structural (FTIR), and thermal gravimetric analysis (TGA) were investigated. Characterization results clearly showed that the method of preparation results in a significant difference in the structure, thermal stability, shape and dimensions of the produced CNFs. TEMPO-mediated oxidation produced brighter and higher yields (>90%) of CNFs compared to other methods. FE-SEM and AFM analysis clearly indicated that, TEMPO-mediated oxidation produced uniform nano-sized fibers with a very small diameter (3-15 nm width) and very small length (10-100 nm). This was the first time uniform and very small nanofibers were produced.